Vehicle cabs are usually built around a frame construction. The look of the frame construction is largely determined by strength requirements which ensure that the cab has good collision characteristics and provides a secure driver's compartment should the vehicle overturn. More particularly, the beams which support the roof of the cab, the roof bars, are configured to resist deformation should the upper part of the cab collide with a fixed object. In modern vehicles, moreover, high demands are placed upon visibility and space. It is therefore desirable for the frame construction to be formed from as narrow of beams as possible. Should the dimensions of the roof bar be reduced, there is a risk of the roof bar being broken off or bent in toward the interior of the cab in the event of collision with a fixed object. Should the roof bar become broken or bent, there is a risk of the upper part of the A-pillar being pressed down and into the cab so that a driver is at high risk of an injury/accident. In order to ensure that bending or breakage shall not take place, roof bars have therefore been made in thick dimensions. This results in increased weight for the cab, whereupon other included beams also have to be made in relatively thick dimensions.